Just spent a bit of time playing around with Sunbird. I would call it “not quite ready for prime time.” It’s got a nice interface. I was able to subscribe to my iCal-published calendar without a hitch. It can auto-reload remote calendars on startup. I can also create local calendars and publish them successfully. However, the publishing support seems to be kind of a work-in-progress. When I publish a new calendar, it doesn’t remember its URL. I have to re-type it every time I publish. When I try to modify a remote calendar that I subscribed to, it crashes. There appears to be no support for auto-publishing as entries are made.
I’ll keep an eye on Sunbird, but it looks like it’s not quite ready for day-in day-out use. I expect it’ll get there eventually though.